1. Field of the Invention
This invention relates to wheel nuts having sheet metal sheaths resistance welded to the nut and to a process of forming such nuts.
2. Prior Art
Most modern automotive wheels are removably attached to the axle by a ring of threaded studs which extend outwardly from conical depressions formed in the axle end. The wheel contains a similar ring of holes formed with conically dished edges which abut the depressions in the axle end so that the studs extend through the wheel holes. Wheel nuts are then threaded on the studs to secure the wheel to the axle. The nuts and extending studs may be surrounded by a dish-shaped cover which attaches to the wheel to hide and protect the nuts and studs. Alternatively, wheel nuts having integral sheaths formed of thin sheet material may be employed. The sheaths cover the exposed nut surfaces and enclose the volume about the end of the nut opposite to that which contacts the wheel. The cap protects the projecting end of the stud from damage due to weathering and impacts. The sheath is typically formed of brushed stainless steel, or plastic, or a combination of the two, for aesthetic purposes.
The sheath or cap must be secured to the nut body to prevent their accidental loosening, particularly under the forces exerted during wrenching of the nuts. Such loosening would cause rattling of the wheel as it rotated and might allow the cap to fall off of the nut. U.S. Patent No. 3,364,806 assigned to the assignee of the present invention, discloses a form of wheel nut wherein the cap is secured to the nut insert by crimping the free end of the cap around the chamfer, or shoulder, formed between the wrench flats and a cylindrical land connecting to the conical end of the nut. Efforts have also been made to secure the cap to the nut body with adhesives because of the low tensile and shear strength of adhesives and because difficulty is encountered in applying sufficient adhesive to securely retain the two without getting the adhesive on the nut threads.
It has also been proposed to weld the cap to the nut. This insures rigid attachment and eliminates the danger of clogging the nut threads with the adhesive, but presents certain problems in application. For one thing, the heat generated in the welding process may adversely affect the heat treatment of the nut, as by unacceptably softening it, and may affect the metallurgy of the cap to discolor it or reduce its oxidation resistance. The present invention is broadly directed toward a form of welded junction between a sheet metal cap and a wheel nut and to a method of forming the weld which eliminates these problems.